Electromechanical security door lock mechanisms actuated by solenoids are ubiquitous. A typical lock mechanism allows a user on one side of a door to mechanically actuate the locking mechanism to release the lock while requiring a user on the other side of the door to actuate it electromechanically with a security device such as a key, a card reader, or a keypad requiring that a password, number or word be entered.
Panic exit devices, for example, employ a mechanical latch release mechanism that allows a user on the egress side of a door to mechanically actuate the mechanism as a fail-safe release for the door latch to allow exit from a room. The Von Duprin company of Indianapolis, Ind. makes several such devices and related components such as their 33A/35A and 98/99 Series Exit Devices. A panic exit device may also be equipped to be actuated electromechanically with a solenoid to allow a person on the opposite ingress side of the door to operate the latching mechanism electrically. A user attempting to operate the latching mechanism from the ingress side might be required to use an electronic security device to gain access such as a card reader or keypad to electromechanically release the latch mechanism. The Sargent Manufacturing Company of New Haven, Conn. makes various electromechanical latching devices using a solenoid actuator, their Series 80 product line is similar to that of the Von Duprin 33A/35A and 98/99 Series products. In some applications the egress latching mechanism may be operated by employing an electromechanical latching mechanism as well, using a solenoid to operate the latching mechanism.
These electromechanical latching devices use a solenoid to actuate the latching mechanism in the door, to move it from a first closed or locked position to a second open or unlocked position. Solenoids are widely used operate a variety of electromechanical door latch configurations. The above panic exit devices for example may be configured to be used with a latching mechanism that includes vertical rods, roller (horizontal) rods, or with rim or mortised types of latching mechanisms. Exemplary prior art designs for latching devices and components of analogous construction are shown in Zawadski U.S. Pat. No. 3,767,238 entitled Push Plate Panic Exit Device and Godec et al, U.S. Pat. No. 4,167,280 entitled Panic Exit Mechanism.
These electromechanical door latching mechanisms require a separate power supply to supply current to operate the solenoid. A typical power supply for a solenoid of the prior art is located at a distance from the latching mechanism on the door itself. A typical power supply is a transformer used to convert 120 or 220 VAC input current to a safe 24 VDC output current to operate the solenoid at its required current load. The solenoids used with these devices require a substantial momentary current load for an interval of time to move the latching mechanism.
A solenoid used in door latches typically include primary and secondary coils that move an armature or plunger and hold the armature of the solenoid in the moved position. The armature is connected to a latching mechanism and the primary solenoid coil causes the armature to move the latching mechanism from a first locked or closed position to a second unlocked or open position. The secondary coil thereafter retains the armature and latching mechanism in the unlocked configuration. Latching mechanisms are typically biased with a spring to return the latching mechanism to the closed or locked position after power to the secondary coil is removed.
The primary coil of a solenoid for a door actuator is typically operated for a load interval of about 10-200 msec at 20-30 VDC, depending on the solenoid being used. The secondary coil requires only perhaps half an ampere at to retain the latching mechanism in an unlocked configuration thereafter.
These devices have proved very useful and successful over the years. Panic exit and security entry devices are a critical part of any fire and safety system and providing restricted access and safe and reliable egress from a building in the event of a fire or power failure. Such devices are frequently required by local fire safety and building codes.
A longstanding problem with the prior art is that the power supply for the latching mechanism must be able to supply power at an acceptably safe lower voltage and with sufficient current to meet the inrush surge current load drawn during actuation of the primary coil of the solenoid. Because the current must be maintained at a safer lower typically 24 VDC voltage to prevent electrocution, the effects of resistance and voltage drop are increased in the transmission of power from the power supply to the solenoid over a transmission wire. Because the output voltage of the power supply must be kept low the effects of resistance and particularly voltage drop in the wire connecting the power supply to the solenoid must be minimized.
Voltage drop is also increased as the power supply is located at greater distances from the solenoid, this requires that the power supply be situated relatively close to the solenoid. Typically the transmission wire connecting the power supply to the door latch solenoid cannot exceed more than twenty-five feet in length and therefore presents an inherent design limitation.
Voltage drop and resistance are also proportional to wire size and the voltage drop in connecting transmission wire has been minimized in the prior art by using a larger gauge wire to connect the power supply to the solenoid. Standard 18-gauge electrical wiring used in buildings is usually unsuitable for carrying the needed momentary current surge load between the power supply and the solenoid of a door latch mechanism so heavier gauge wiring, 12-gauge wire for example, is typically used instead. This heavier wire must be specially installed in the walls between the power supply and the solenoid of the door. The need to install heavier gauge wiring to carry current between the power supply and the door solenoid is costly and laborious.
What is needed then is a way to reduce voltage drop in the transmission wire without the necessity of using heavier gauge wire and without the necessity the need for the power supply be in such close proximity to the solenoid. This would allow for a wider choice of locations for the power supply and be more economical as well because a lighter gauge wire may be used.
Further objects and advantages of the invention will become apparent to one skilled in the art by reading and understanding the following summary, detailed description and the drawings to which it refers.